Like many Pokémon games, Pokémon X & Y introduce various Pokémon with differences depending upon whether or not the Pokémon are male or female. These differences used to be cosmetic but Pokémon X & Y follows on from the precedent set in Black & White and furthers these considerably.

Meowstic

Details:
Meowstic's gender difference is rather unique in that not only is the appearance altered, it will learn different moves depending upon which gender it is. This makes the gender difference act almost as if it was a separate Pokémon. The male Meowstic acts more of a supporter while the female is an attacker

Male

Female

MovesMiracle Eye

MovesExtrasensory

Pyroar

Details:
Pyroar's gender difference is a bit less unique and only affects the Pokémon's appearance. When male, it is said to be the leader of the pack while the female of the pride is tasked to protect its young